The present invention relates to a camera with a changeable focal length, and more particularly to a focal length changeable camera equipped with a motor drive mechanism by which a taking lens system is changed in focal length.
Recent compact cameras are equipped with taking lens systems of the type in which the focal length can be changed between various focal lengths, for example between a relatively short focal length of approximately 35 mm suitable for wide-angle photography and a relatively long focal length of approximately 70 mm suitable for telephotography. Such focal length changeable cameras have taking lens systems which generally include an axially movable master lens and an extra lens which is displaced from or moved into the optical path of the taking lens system upon changing the taking lens system to the relatively long focal length.
In one instance of such a focal length changeable camera disclosed in, for example, Japanese Unexam. Patent Publ. No. 60-114,836 there is provided a toggle spring to thrust back and forth the axially movable master lens in the direction of the optical path or to extend it from and retract it into the camera body so as to change the focal length of the taking lens. The provision of such a toggle spring makes focal length changeable cameras simple in structure but needs relatively large force to thrust back and forth the master lens for the change of focal length.
In another instance, as is disclosed in Japanese Unexam. Patent Publs. Nos. 60-163,010 and 61-35,435, a motor for advancing or transporting a film in the camera is commonly used to thrust back and forth the axially movable master lens. The motor is operationally coupled to a movable lens barrel holding the master lens through a one-way clutch comprising, for example, a planetary gearset. Therefore, such motor driven focal length changeable cameras need not only a reverse switch for reversing the motor in rotation but also a self-housing switch for maintaining the motor reversed. In order to control the operation of these switches, it is necessary to provide a mechanism including, for example, cams and levers which will generally make the internal mechanisms of the camera complicated.
Otherwise, the one-way clutch coupling the lens barrel to the motor is maintained coupled by a self-holding member which is brought into operation through an axially movable member in cooperation with the axial movement of the lens barrel. In this instance, the lens barrel will receive undesirable external force exerted thereon at angles to the optical axis of the taking lens system. Such undesirable external force causes the optical axis of the taking lens system to deflect or incline. Therefore, it is necessary to provide means such as rollers for the prevention of such deflection or inclination of the optical axis of the taking lens system.
It is also necessary to provide position sensors such as a limit switch in association with the master lens or its lens barrel in order to detect whether the master lens or the lens barrel is at one of two possible lens positions, or at a position between the possible lens positions, thereby stopping the motor. The provision of such position sensors will also make the internal mechanism of the camera complicated.
Furthermore, it is necessary to provide electrical or mechanical interlock means for preventing a shutter release button or a focal length change member from being operated during the time the focal length change member is being operated to change the focal length of the taking lens system or during the time the shutter release button is being operated, respectively. An electrical interlock means is necessary, which cooperates with a position sensor or sensors such as a limit switch in association with the master lens or its lens barrel in order to detect whether the master lens or the lens barrel is at one of two possible lens positions, or at a position between the possible lens positions, thereby stopping the motor. The provision of such position sensors will also make the internal mechanism of the camera complicated.